The fourth quarter always sneaks up. Most business owners are heads-down on holiday staffing, year-end sales pushes, or client work, and tax deadlines end up on a sticky note instead of a calendar. But the stretch between October and January carries more tax deadlines than any other three months of the year, and missing one is rarely cheap.

Here is what Ohio business owners should have on their radar before 2026 closes out — and just after.

December 15, 2026 — Q4 estimated tax payment for calendar-year corporations

If your business operates as a C corporation on a calendar year, your fourth and final estimated tax installment for 2026 is due December 15, not January. This is one of the more commonly missed dates, because it doesn't line up with the individual estimated tax schedule, and owners who also file personally sometimes assume both land in January.

December 31, 2026 — Year-end payroll and retirement account deadlines

If you're planning year-end bonuses or additional owner compensation, the payment needs to actually hit before December 31 to count for the 2026 tax year — accruing it on paper isn't enough for most structures. December 31 is also the deadline to take a 2026 required minimum distribution from a retirement account for owners age 73 or older.

January 15, 2027 — Q4 estimated tax payment for individuals, partnerships, and S corporations

This is the one most owners have circled: the fourth-quarter estimated payment for individuals and pass-through entities — partnerships, S corporations, and LLCs taxed as either. It covers income earned September through December 2026. If you file your 2026 return and pay in full by February 2, 2027, you may not need to make this payment separately — but don't assume that exception applies to you without checking with your accountant first.

January 31, 2027 — W-2s and 1099s due to recipients

If you had employees or paid an independent contractor $600 or more in 2026, W-2s and 1099-NEC forms need to be in their hands — not just prepared — by this date. This is also generally the filing deadline for these forms with the Social Security Administration and IRS.

Looking ahead: March and April 2027

Partnerships and S corporations should plan for a March 16, 2027 filing deadline (Form 1065 or 1120-S). C corporations and sole proprietors file by April 15, 2027, which is also the deadline for the first 2027 individual estimated tax payment. If you're weighing an S-corp election for 2027, the deadline to file Form 2553 for an existing calendar-year entity generally falls around that same March date — so that decision needs to happen well before the year-end rush.

Practical takeaway

None of these dates is complicated on its own. What gets business owners in trouble is treating “tax season” as one event instead of a sequence of separate obligations spread across four months. Put December 15, December 31, January 15, and January 31 on your calendar now, and loop in your accountant early if any of them touch owner compensation, bonus timing, or an entity election you've been putting off.

Sources and further reading

●       IRS Q4 Tax Calendar

●       IRS Form 1040-ES, Estimated Tax for Individuals

●       IRS Instructions for Form 2553, Election by a Small Business Corporation

If you want a second set of eyes on your year-end tax positioning or an upcoming entity election, we're happy to help — schedule a consultation online or reach our office at 216-644-3359.